The invention relates to plug-in unit assemblies comprising instrument transformers, and particularly to protective relay assemblies comprising a plug-in unit.
Different protective relay versions comprise a varying number of current and voltage transformers. Their connectors are subject to the requirement that the current circuits must close when the plug-in unit is being extracted, but, correspondingly, the voltage circuits must not short. In known solutions, a connector adapted to connect current and voltage transformers has to be assembled for each combination from different current and voltage connector components and, in addition, the modules have to be coded in order to prevent a module from being inserted into the wrong connection slot.
The problem in the above-described arrangement is that current and voltage transformers require different mating connectors. Another problem is the cost caused by the coding of modules. For example, if an as sembly comprises six transformer slots having current or voltage transformers, the number of combinations is large, requiring an expensive mechanical coding system including set-ups and maintenance.